The present disclosure relates to devices and methods that permit fixation and stabilization of the bony elements of the skeleton of a patient. The devices permit adjustment and maintenance of the spatial relationship(s) between neighboring bones. Depending on the specifics of the embodiment design, the motion between adjacent skeletal segments may be limited or completely eliminated.
Spinal degeneration is an unavoidable consequence of aging and the disability produced by the aging spine has emerged as a major health problem in the industrialized world. Alterations in the anatomical alignment and physiologic motion that normally exists between adjacent spinal vertebrae can cause significant pain, deformity, weakness, and catastrophic neurological dysfunction.
Surgical decompression of the neural tissues and immobilization of the vertebral bones is a common option for the treatment of spinal disease. Currently, vertebral fixation is most frequently accomplished by anchoring bone screws into the pedicle portion of each vertebral body and then connecting the various screw fasteners with an interconnecting rod. Subsequent rigid immobilization of the screw/rod construct produces rigid fixation of the attached bones.
A shortcoming of the traditional rod/screw implant is the large surgical dissection required to provide adequate exposure for instrumentation placement. The size of the dissection site produces unintended damage to the muscle layers and otherwise healthy tissues that surround the diseased spine. A less invasive spinal fixation implant would advantageously minimize the damage produced by the surgical exposure of the spine.
In U.S. Pat. No. 7,048,736, Robinson et al teach the use of interspinous process plate to fixate adjacent vertebrae. As disclosed, the device is used to supplement orthopedic implant and for bone graft material placed into the intervertebral disc between the attached vertebra. Thus the device functions to immobilize the vertebrae until bone fusion occurs but, in itself, does not provide a compartment for bone graft placement within the posterior aspect of the spine. Since bone graft material must be placed in order to achieve vertebral fusion, the device must be used in conjunction with bone graft material that is placed at a secondary site of the attached vertebra bones, such as within the disc space, between adjacent transverse processes, and the like. This is a significant disadvantage and prevents use of the Robinson device by itself to both immobilize and fuse the vertebral bones.
The growing experience with spinal fusion has shed light on the long-term consequences of vertebral immobilization. It is now accepted that fusion of a specific spinal level will increase the load on, and the rate of degeneration of, the spinal segments immediately above and below the fused level. As the number of spinal fusion operations have increased, so have the number of patients who require extension of their fusion to the adjacent, degenerating levels. The rigidity of the spinal fixation method has been shown to correlate with the rate of the degenerative progression of the adjacent segments. In specific, implantation of stiffer instrumentation, such as rod/screw implants, produced a more rapid progression of the degeneration disease at the adjacent segment than use of a less stiff fixation implant.